1. Field of Invention
The present invention relates to a method for driving an organic light emitting display (OLED) panel. More particularly, the present invention relates to a pulse width modulation method for driving an OLED panel.
2. Description of Related Art
Flat panel displays are generally classified into inorganic devices and organic devices according to the display materials used in the flat panel displays. The inorganic devices include plasma display panels, field emission displays and the like; the organic devices include liquid crystal displays, organic light emitting displays (OLED) and the like. The OLED is in the spotlight because of its operating speed being faster than that of the liquid crystal display by thirty thousand times. In addition, the OLED has advantages of wide viewing angle and high brightness due to emitting light by itself.
FIG. 1 is a schematic view of a conventional OLED 100. An OLED panel 110 has a plurality of organic light emitting diodes 112, which are driven by a segment driver 120 and a common driver 130 through segment lines 122 and common lines 132. Particularly, the organic light emitting diodes 112 are electrically connected to the segment lines 122 and common lines 132 in a matrix structure. In the prior art, a pulse width modulation (PWM) manner is provided to supply driving currents to the organic light emitting diodes 112. The driving currents of the PWM manner may have different pulse widths. The pulse width determines the intensity of the light emitted from the organic light emitting diode 112.
FIG. 2 is a schematic view of waveforms provided by a conventional PWM manner, in which the waveforms GS1 to GS4 of 2-bit grayscales are illustrated as an example. In a period, the pulse widths of the waveforms GS1 to GS4 are altered in accordance with different grayscales. However, the rising edges of the waveforms corresponding to different grayscales are all positioned at a starting time t0 of the period T. The coherent rising of the waveforms GS1 to GS4 causes a peak current to be generated at the starting time t0 of the period T. The peak current increases the required Vcc of the segment driver 120 (as illustrated in FIG. 1), and the power consumption of the OLED 100 is thus raised.
FIG. 3 is a schematic view of waveforms provided by another conventional PWM manner, in which the waveforms GS1 to GS4 of 2-bit grayscales are illustrated as an example. In this PWM manner, the rising edges of the waveforms GS1 to GS4 corresponding to different grayscales are changed from the starting time t0 to other times (e.g. t1 and t3) of the period T. The peak current caused by the coherent rising of different grayscale waveforms GS1 to GS4 is therefore decreased. Nevertheless, if the organic light emitting diodes 112 electrically connected to the same common line 132 (as illustrated in FIG. 1) are simultaneously represented by the same grayscale, the driving currents having the same waveform are supplied at the same time. Consequently, the peak current issue still remains.